Bears could be looking for human sources of food more often than usual.

The hard frost that killed a good portion of this year’s berries, acorns and chokecherries has pushed bears ever closer to populated areas.

The consequences of venturing farther afield has been particularly evident.

Bears are being struck and killed by vehicles as they cross major highways.

Six bears were killed by vehicles in the region through July, state Parks and Wildlife spokesman Joe Lewandowski said Tuesday. The count for this month won’t be known until next week, he said.

Bryan Peterson of Bear Smart Durango, a program to educate residents about coexisting with bears, said from Aug. 13 to Saturday, four bears were killed by vehicles on U.S. Highway 550 north of Durango, and one was killed on U.S. Highway 160 west.

Peterson said vehicles killed 10 bears in 2010 and 16 last year. The total number of bears killed in 2011 was 36, including one killed by landowners and the state wildlife personnel.

Heather Johnson, a Parks and Wildlife biologist who is leading a multi-year study of bears in La Plata County to establish their numbers and learn their habits, has lost three ursines to vehicles.

Adult females are fitted with a radio collar. Males and young bears get an ear tag.

As fall approaches, bears know it’s time to pack on calories to get them through the winter. The urgency to increase daily food intake to 20,000 calories – the equivalent of 70 cheeseburgers – sends them into urban areas more frequently than usual.

“A bear is 80 percent herbivore, 20 percent carnivore,” Patt Dorsey, Parks and Wildlife area wildlife manager in Durango, said Tuesday. “They like ants and bee larvae, but they eat carrion such as road kill, too.”